The present invention relates to a chuck actuator. More particularly this invention concerns such an actuator for a pivot chuck where the actuating member must be able to move along its rotation axis to open and close the chuck and rotate about its axis to pivotally switch the chuck jaws.
A standard pivot chuck such as described in German patent document 3,215,899 of Kimm, German patent 3,230,135 of Muller, and U.S. Pat. No. 4,747,609 of Scharfen has a jaw assembly that is tightened and closed by axial movement of an actuating member, typically a rod that extends along the chuck rotation axis from an actuator housing to which a chuck body carrying the jaws is fixed. This actuating rod is advanced to open or spread the jaws and retracted to close them together. The jaws are in turn mounted on an intermediate part that can be pivoted about an axis transverse to the chuck pivot axis to reposition the work-piece so that, once the work-piece is secured in the chuck, it can be machined from opposite ends or in different positions.
The pivoting action is typically controlled by rotation of the actuating rod about its axis, allowing this part to serve a second function. To this end the actuating rod carries in the chuck member a main piston centered on the chuck axis and movable axially in a cylinder for opening and closing the chuck, and a radially projecting vane element angularly subdividing another chamber into a pair of compartments alternately pressurizable to rotate the actuating rod.
The angular position of the vane thus can change so that it presents an eccentric mass whose position similarly changes depending on chuck setting. Attempts to counterbalance this eccentric mass have been only marginally effective. Chuck rotation speeds are therefore limited to at most 2000 rev/min which is often not fast enough for some high-speed machining operations.
It is therefore an object of the present invention to provide an improved pivot-chuck actuator.
Another object is the provision of such an improved pivot-chuck actuator which overcomes the above-given disadvantages, that is which can be operated at very high rotation speeds.
A pivot-chuck actuator has according to the invention a housing extending along an axis and formed centered on the axis with a piston chamber and with a vane chamber offset and separate from the piston chamber. A piston axially displaceable in the piston chamber is axially fixed to a shaft extending from the housing on the axis. A vane element on the shaft angularly subdivides the vane chamber into a pair of angularly offset compartments and formations rotationally couple the vane element to the shaft for joint rotation therewith while permitting relatively axial movement of the vane element and shaft. The compartments cam be alternately pressurized to rotate the vane element and shaft about the axis. A pair of counterweights angularly fixed on the shaft axially flank the vane element.
Using two counterweights axially flanking the vane element allows its weight to be very effectively counterbalanced so as to meet DIN ISO 1940 for G=6.3 or more. The actuator can spin at 4000 rev/min without difficulty.
According to the invention formations rotationally couple the counterweights to the shaft for joint rotation therewith while permitting relative axial movement of the counterweights and shaft. The housing is further formed with respective counterweight chambers axially flanking the vane chamber and receiving the counterweights. These chambers are filled with oil and the counterweights are formed with angularly throughgoing passages. Thus the counterweights damp rotation of the shaft. Furthermore the axial positions of the counterweights and vane element remain fixed, even if the shaft moves axially, to main-tain perfect counterbalance.
Each of the counterweights according to the invention is formed, line the vale element, as a rectangular arm projecting radially from an annular hub the shaft and having a rounded outer end. Furthermore the counterweights are of identical shape and mass, normally made of the same metal. In fact each counter-weight can, seen axially, be of a shape identical to that of the vane element but can have an axial length equal to half that of the vane element. The formations rotationally coupling the counterweights to the shaft are respective pins set in the shaft and axially extending grooves receiving the pins and formed in the counterweights.
The counterweights in accordance with the invention project 180xc2x0 offset from the vane element. The housing is formed by a plurality of axially stacked plates. Furthermore the housing is formed with a tubular stem coaxially surrounding the shaft. The pressurizer includes a distributor rotatable on the stem and passages formed in the stem.